1. Field of the Invention
The invention generally relates to energy management systems, and more specifically to the monitoring of energy consumption by temperature controlled equipment having operational cycles.
2. Prior Art
Many electrical devices cycle periodically between operation, i.e., on mode, and non-operation, i.e., off mode, states. This operating scheme is typical, for example, to temperature controlled equipment such as compressors that are used for refrigeration or heating, ventilation and air-conditioning (HVAC) equipment. By analyzing these cycles, it is possible to detect or predict equipment failures, and by that achieve significant savings in energy and capital.
A typical and very simple example is equipment that stops from cycling and is in a continuous ‘on’ state (continuously active). In compressors comprised within HVAC systems, for example, this can be sometimes a result of a broken contact in the temperature control circuit, too low temperature set point, if a unit that is under-sized relative to the cooling space and more. Another example is equipment that shows excessive cycling (too many cycles per day) or excessive short cycles (i.e., cycles in which the ‘on’ state lasts only a short period of time, e.g., a few minutes). Since most cooling systems take several minutes to reach at steady state after the compressor starts, compressor run times of less than ten minutes may indicate a problem in the system. This condition is typically caused by gross equipment oversizing, poor thermostat location, coil blockage, condenser fan problems or compressor problems and more.
The above cycle analysis requires circuit level real time monitoring that can be achieved by placing various monitors such as self-powered power sensors (SPPSs). It would be advantageous to use the data collected by such monitor devices for the purpose of energy savings as well as failure detection, preventative maintenance and prediction in cycling equipment.